Encyclia pygmea "in situ"

Cool!

 

cleis·tog·a·mous(kl -st g -m s) also cleis·to·gam·ic(kl st -g m k)
adj. Botany
Of or relating to a flower that does not open and is self-pollinated in the bud.

I've never heard of that before. I'm assuming it is not very common. Are there many other orchids that do that? What is the reason that a plant would do this? Evolution?
Thanks!

 

Many clones of Den. delicatulum have the bad habit of being cleistogamous as well. Perhaps it is due to pollinators being in short supply, so the plants have taken it upon themselves to reproduce somehow. I'd imagine populations where this takes place would have very low genetic diversity between individuals, though.

 

I think it's fascinating when orchids make these changes. We're talking thousands of years of evolution to do this right? I mean how do they get by in the meantime? I know it's got to be complicated but what's the process of changing when the plant realizes it needs to do something to survive? It just can't happen over night and what about survival in the interim? Did I already say that?

 

I don't think it would necessarily take thousands of years to see this. While it is true that most evolutionary events take a very long time, scientists are now recognizing a phenomenon know as instantaneous speciation...an event where a random mutation, etc. causes one population to diverge from another within a very short period of time.

The thing about evolution is that it isn't a need-based change. The plants don't "know" their pollinators are going extinct, so they decide to change. A change in the environment, though, can favor certain traits in a specific individual or population, resulting in them having differential reproductive success.

A theoretical scenario for the appearance of cleistogamous flowers could go like this... A species of orchids depends on a specific insect pollinator to pollinate their flowers. This orchid species has two disjunct populations on neighboring mountain slopes. These populations are relatively close to one another, but due to being on different mountains, gene flow between the two of them has stopped. Population A lives in a national park where all wildlife is protected. Population B lives near a rural village with heavy agricultural activity. General insecticides are sprayed in the rural area, wiping out the insect pollinator in Population B. Pop. A continues on and remains healthy, but Pop. B begins to decline over a few generations due to old plants dying and no seedling recruitment. Then, with a strange twist of fate, one plant in Pop. B develops a totally random mutation which causes the male and female floral parts develop unusually close together, resulting in self-pollination before or shortly after the flower opens. This plant is the only one in the population able to reproduce, and the self-pollinating trait is passed down to some of the offspring. Over a few generations, the cleistogamous plants are the only remaining individuals in Pop. B, and Pop. A remains normal.

Hopefully, this helps out a bit. I kind of made it up on the fly!

 

I know you are creating a fictitious scenario so for the sake of argument, was the mutation a "convenient accident" or was there something inside the living energy of the plant that realized the situation and somehow created the mutation. I mean I've always believed there is some "intelligence" in orchids because on all the different plants that mimic the pollinator or create the smell to attract the pollinator etc. or something. I don't think these are just coincidences, do you?

 

No, it is pretty widely accepted that mutations are totally random. The fact that there are both negative and positive mutations tends to support the fact that they are random and not just simply turned on or off.

Plant-pollinator interactions go well beyond the realm of orchids. Take a look at all the aroids (Amorphophallus is one genus that comes to mind) that smell like rotten meat or all of the tube-shaped, brightly colored flowers that attract butterflies or hummingbirds. Many Malagasy plants are pollinated only by lemurs. The phenotypes that we observe today are simply generations and generations of co-evolution, which often selects for the most extreme phenotype (the longest spurs pollinated by the longest moth proboscis) in both parties. This co-evolution also occurs in antagonistic relationships such as those between predators and prey. A classic example is the evolutionary arms race between the garter snake and newt. Here is a link that gives a little more explanation.

EDIT: The site is linked to the word "here" above. Is there a way to have linked words change color or be highlighted to alert readers that there is a link attached?

 

Thanks Marni! I took a class on evolution last semester, and it wasn't nearly as interesting as I'd hoped. I did, however, love the 1/3 of the class where we learned co-evolution, mutualistic-antagonistic relationships, mimicry and speciation. The garter snake vs. newt arms race was one of the examples we were taught. The relationship between coral snakes and their mimics and also how the cane toad has affected Australian predators were two other topics I found very interesting. I can find links if anyone is interested in reading further.

 

For what it is worth, cleistogamy is pretty common throughout the plant kindom. For many plants there are sub-populations that show cleistogamy, and other populations that do not. Sometimes the same plant will exhibit the trait in one flower but not another. For example soyabeans, fully 60% of soyabean flowers self pollinate, but outcrossing is possible.

Phrag extaminodium and lindenii self pollinate
Cattleya aurantiaca has populations that are cleistogamous. We only collect the ones that open their flowers.
The list is very long. Its a common occurance.